Module: Gitlab::Usage::Metrics::Aggregates::Sources::Calculations::Intersection

Included in:
PostgresHll, RedisHll
Defined in:
lib/gitlab/usage/metrics/aggregates/sources/calculations/intersection.rb

Instance Method Summary collapse

Instance Method Details

#calculate_metrics_intersections(metric_names:, start_date:, end_date:, recorded_at:, subset_powers_cache: Hash.new({})) ⇒ Object 



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# File 'lib/gitlab/usage/metrics/aggregates/sources/calculations/intersection.rb', line 10

def calculate_metrics_intersections(metric_names:, start_date:, end_date:, recorded_at:, subset_powers_cache: Hash.new({}))
  # calculate power of intersection of all given metrics from inclusion exclusion principle
  # |A + B + C| = (|A| + |B| + |C|) - (|A & B| + |A & C| + .. + |C & D|) + (|A & B & C|)  =>
  # |A & B & C| = - (|A| + |B| + |C|) + (|A & B| + |A & C| + .. + |C & D|) + |A + B + C|
  # |A + B + C + D| = (|A| + |B| + |C| + |D|) - (|A & B| + |A & C| + .. + |C & D|) + (|A & B & C| + |B & C & D|) - |A & B & C & D| =>
  # |A & B & C & D| = (|A| + |B| + |C| + |D|) - (|A & B| + |A & C| + .. + |C & D|) + (|A & B & C| + |B & C & D|) - |A + B + C + D|

  # calculate each components of equation except for the last one |A & B & C & D| = (|A| + |B| + |C| + |D|) - (|A & B| + |A & C| + .. + |C & D|) + (|A & B & C| + |B & C & D|) -  ...
  subset_powers_data = subsets_intersection_powers(metric_names, start_date, end_date, recorded_at, subset_powers_cache)

  # calculate last component of the equation  |A & B & C & D| = .... - |A + B + C + D|
  power_of_union_of_all_metrics = subset_powers_cache[metric_names.size][metric_names.join('_+_')] ||= \
    calculate_metrics_union(metric_names: metric_names, start_date: start_date, end_date: end_date, recorded_at: recorded_at)

  # in order to determine if part of equation (|A & B & C|, |A & B & C & D|), that represents the intersection that we need to calculate,
  # is positive or negative in particular equation we need to determine if number of subsets is even or odd. Please take a look at two examples below
  # |A + B + C| = (|A| + |B| + |C|) - (|A & B| + |A & C| + .. + |C & D|) + |A & B & C|  =>
  # |A & B & C| = - (|A| + |B| + |C|) + (|A & B| + |A & C| + .. + |C & D|) + |A + B + C|
  # |A + B + C + D| = (|A| + |B| + |C| + |D|) - (|A & B| + |A & C| + .. + |C & D|) + (|A & B & C| + |B & C & D|) - |A & B & C & D| =>
  # |A & B & C & D| = (|A| + |B| + |C| + |D|) - (|A & B| + |A & C| + .. + |C & D|) + (|A & B & C| + |B & C & D|) - |A + B + C + D|
  subset_powers_size_even = subset_powers_data.size.even?

  # sum all components of equation except for the last one |A & B & C & D| = (|A| + |B| + |C| + |D|) - (|A & B| + |A & C| + .. + |C & D|) + (|A & B & C| + |B & C & D|) -  ... =>
  sum_of_all_subset_powers = sum_subset_powers(subset_powers_data, subset_powers_size_even)

  # add last component of the equation |A & B & C & D| = sum_of_all_subset_powers - |A + B + C + D|
  sum_of_all_subset_powers + (subset_powers_size_even ? power_of_union_of_all_metrics : -power_of_union_of_all_metrics)
end